The use of ball grid arrays (BGAS) to package electronic circuits and devices such as integrated circuit chips is becoming more prevalent. BGA packaging has proven to provide substantial advantages over other packaging techniques such as, for example, dual in-line packages (DIPs), pin grid array (PGA) packages, tape carrier packages (TCPs), and quad flat packs (QFPs). The advantages of BGA packaging become especially significant when used to package an integrated circuit chip or die having a high pin count and when used to package devices employing high frequency signals. BGA packaging provides the additional advantage of being able to use conventional surface mount technologies (SMTs) and assembly techniques when mounting to a printed circuit board (PCB).
A BGA package generally includes a die or chip, one or more substrate layers provided on top of one another and aligned through a cavity portion, an array of solder balls for providing an electrical and mechanical connection external to the BGA package, and a heat spreader/stiffener for providing a thermal conduction path to cool the die and to provide mechanical support and rigidity to the BGA package. The substrate layers include various metal layers and traces that serve as signal and/or power distribution connections in addition to distinct signal and power planes. Each of the solder balls of the array of solder balls electrically couple to either ground pads, power pads, or signal pads on the exposed substrate. Solder balls may also couple to sacrificial pads that are provided for mechanical advantages and do not provide an electrical connection to the package. The electrical connections are generally made through vias or metallized interconnections provided through the various substrate layers. The fabrication of the various vias and substrate layers is expensive and time consuming and reduces the overall packaging yield and reliability of high pin-count packages.
The die is generally mounted on the heat spreader/stiffener using an adhesive or glue such as an epoxy. The various bond pads of the die are electrically coupled to the various solder balls of the array of solder balls by coupling to either the ground plane, the power plane, or to a corresponding signal trace provided by the signal plane. The connection is generally provided using wire bonding techniques. These connections are expensive and complicated by the fact that connections must be made with multiple substrate layers.
The fabrication of the multiple metal layers, traces, and multiple substrate layers is expensive. The complexity and cost of EGA packages are also influenced by the number of signal layers and vias that must be provided in the various substrate layers to provide a path to connect the solder balls to either the ground plane, the power plane, or a desired signaling lead of the signal plane. In general, multiple substrate layers and multiple vias result in lower BGA package fabrication yields and higher costs.
The formation of the vias create additional complexity and cost because each of the vias generally require the formation of a conductive layer, such as a metal layer on the internal walls of the via, to ensure a complete electrical path. This may be referred to as metallization. The metallization of the internal walls of each via increases the overall complexity and cost of manufacturing multiple substrate layer BGA packages.